This invention relates to a biological filter apparatus with multiple filter units, and to a method of operating a biological filter apparatus.
The copending application, the entire disclosure of which is hereby incorporated by reference herein, discloses a biological filter apparatus that comprises a trickling filter unit and a biological filter unit. The tricking filter unit includes a biologically inert filter bed whereas the biological filter unit includes a filter bed that contains organic compost containing a population of microorganisms that have an affinity for volatile organic compounds (VOCs) and consume VOCs and nutrients present in the compost. Each filter unit includes a spray tube for spraying water onto the filter bed. The water passes downwards through the filter beds and is collected in sumps beneath the two filter beds respectively. The sumps of the two filter units are in fluid communication, and water is drawn from the sump of the trickling filter unit for spraying onto both the inert filter bed and the biologically active filter bed. Because the two sumps are in fluid communication, the water that is sprayed onto the inert filter bed contains compost that has eroded from the biologically active filter bed. Accordingly, the inert filter bed is inoculated with microorganisms from the biologically active filter bed. Air laden with VOCs passes upwards through the trickling filter unit and then passes upwards through the biologically active filter unit. The inoculum in the inert filter bed metabolizes water soluble VOCs, such as certain alcohols, present in the feed air stream, thus reducing the concentration of water soluble VOCs in the air stream before it reaches the biofilter. In this manner, the population of microorganisms in the biologically active filter bed becomes conditioned to remove the water insoluble VOCs.
In accordance with a first aspect of the invention there is provided a filter apparatus for processing air laden with volatile organic compounds, the apparatus comprising a first filter unit defining a first filter chamber and having a first air inlet for admitting air into the first filter chamber and a first air outlet for exhausting air from the first filter chamber, a second filter unit defining a second filter chamber, a second air inlet for admitting air into the second filter chamber and a second air outlet for exhausting air from the second filter chamber, a third filter unit defining a third filter chamber, a third air inlet for admitting air into the third filter chamber and a third air outlet for exhausting air from the third filter chamber, the third inlet being connected to the second air outlet, a biologically inert filter media in the first filter chamber,
a biologically active filter media in the second filter chamber, and a biologically inert filter media in the third filter chamber, whereby air passing through the apparatus passes sequentially through the first biologically inert filter media, the biologically active filter media and the second biologically inert filter media.
In accordance with a second aspect of the invention there is provided a method of processing air laden with biodegradable VOCs, said method comprising (a) passing the air sequentially through first, second and third filter beds, the first and third filter beds each containing a biologically inert filter media and the second filter bed containing a biologically active filter media, (b) collecting water that drains from the first and second filter beds, (c) supplying water collected in step (b) to at least one of the first and second filter beds, (d) collecting water that drains from the third filter bed, and (e) supplying water collected in step (d) to the third filter bed.
In accordance with a third aspect of the invention there is provided a filter apparatus for processing air laden with volatile organic compounds, said apparatus comprising a first wall means defining first, second and third filter chambers, a first air inlet for admitting air to the first filter chamber, a first air outlet for exhausting air from the first filter chamber, a second air inlet, connected to said first air outlet, for admitting air leaving the first filter chamber to the second filter chamber, a second air outlet for exhausting air from the second filter chamber, a third air inlet, connected to said second air outlet, for admitting air leaving the second filter chamber to the third filter chamber, and a third air outlet for exhausting air from the third filter chamber, a biologically inert filter media in the first filter chamber, a biologically active filter media in the second filter chamber, a biologically inert filter media in the third filter chamber, a first water supply means for supplying water to an upper region of at least one of the first and second filter chambers, a second wall means defining a first sump for receiving water from a lower region of at least one of the first and second filter chambers, a first recirculation means for feeding water from the first sump to the first water supply means, a second water supply means for supplying water to an upper region of the third filter chamber, a third wall means defining a second sump for receiving water from a lower region of the third filter chamber, and a second recirculation means for feeding water from the second sump to the second water supply means.